The invention relates to a device for punching blanks out of a flat sheet, in particular packaging blanks consisting of cardboard or corrugated cardboard, by means of a punching tool which is mounted in a carrier plate and projects beyond said plate in the form of a blade or cutting line, and also profiled strips consisting of a material of limited flexibility which flank said tool.
Such devices, in which the tools made of steel strip slide along lateral profiled strips consisting of rubber or flexible plastic, are known in the packaging industry. These profiled strips are either adhesively bonded over their surface to the carrier plate—which is made of plywood for example—or are inserted by beads made in them into grooves of the carrier plate. Laser cuts are made in said plywood plate in order to accommodate so-called cutting lines.
By virtue of this device, packaging blanks can be cut in groups out of a cardboard or corrugated cardboard sheet. The punching machine processes the so-called printed sheets in a cyclical manner; the cutting contours and scoring lines are mainly produced in the punching section thereof.
In order to further transport the punched sheet, so-called supporting points are required which hold the individual packagings together, said packagings also being referred to as copies. When the cutting lines penetrate into the sheet material, very high wedge forces develop which try to destroy the supporting points. By applying the abovementioned elastic profiled strips which run on either side of the punching tool, by virtue of the elastic pressure coming therefrom a higher frictional resistance is produced between the underside of the punched sheet and the surface of the punching plate, and this prevents bursting of the supporting points. The cross section of the elastic profiled strip should in this case be selected such that forces additionally act in the direction of the tool.
One disadvantage of systems known to date is that the profiled strip has to be removed in the event of tool repairs or when forming supporting points. This is difficult in particular since the wood breaks open and profiled parts remain on the wood, and this necessitates cleaning of the surface. Moreover, the base of the profiled strip is lost and the new profiled strips must be inserted, wherein the curing time of the adhesive gives rise to a downtime of the machine.
Knowing these conditions, the inventor set himself the aim of eliminating the known drawbacks, of simplifying the handling of the machine parts and of achieving an improvement in terms of production.